The invention is directed to a process for increasing the stability of hydrolyzable organophosphorous ligands that are used in homogeneous catalysis.
Catalysts comprising a hydrolyzable organophosphorous ligand complexed with a transition metal, such as cobalt or rhodium, are used in many hydroformylation processes. The hydrolyzable organophosphorous ligand can be depleted via an autocatalytic reaction with other components of the hydroformylation reaction mixture.
U.S. Pat. Nos. 5,364,950 and 6,693,219 teach the use of an epoxide to remove acidic impurities in hydroformylation catalyst mixtures to prevent the buildup of acidic materials that cause the autocatalytic decomposition of hydrolyzable phosphorous ligands. U.S. Pat. Nos. 5,741,944 and 5,731,473 teach the use of an aqueous buffer extraction process to remove acids from a hydroformylation catalyst mixture. U.S. Pat. No. 5,767,321 discloses removing acidic impurities by either buffer washing or epoxide addition.
However, the prior art processes do not adequately deal with situations in which high amounts of acid are present, e.g., situations where process variations exist as a result of a process “upset” as in, for example, the case of a temporary extractor failure, the case of a problem with the buffer formulation, or the case of inadvertent addition of acid, etc.
High acid concentrations lead to the loss of highly expensive catalytic metal, which is detrimental to the economics of any commercial process. It would be desirable to have a process for mitigating the presence of acid impurities that (1) treats and removes the acid impurities in the entire reaction system, e.g., in the reactor and in peripheral equipment, and (2) is capable of rapid response to sudden acid increases.